How to make a VSE scene strip render with the openGL render?
In Blender 2.76 or later you can render a Scene Strip in the VSE using OpenGL by hitting one of the two Buttons next to "Use Backdrop". The left one will render a single frame, the right one the entire animation.



In case you want to have transparency for the VSE OpenGL render, it seems you have to set the alpha mode of the OpenGL render options to transparent before adding the scene to the VSE when using 2.79 (Render -> OpenGL Render Options -> Alpha Mode -> Transparent).